The sciatic nerve innervates the thigh flexors, the deep peroneal nerve of the common peroneal nerve innervates the anterior calf muscles, the foot muscles and the peroneus longus and shortus muscles, and is responsible for dorsiflexion and valgus of the foot, extension and toe extension movements, and the superficial peroneal nerve is responsible for sensation of the anterolateral calf and the skin of the foot. The motor fibers of the tibial nerve innervate the gastrocnemius, hallux valgus, flexor digitorum longus, flexor digitorum longus, and posterior tibial muscles, and are involved in plantarflexion, toe flexion, and inversion of the foot; its sensory fibers are distributed in the skin of the lateral foot, sole, and heel. Etiology Sciatica is a syndrome in which the sciatic nerve pathways and distribution areas are predominantly painful, with a variety of causes. The majority of cases of sciatica are secondary to the stimulation and compression of the sciatic nerve by local lesions of the sciatic nerve and surrounding structures, called secondary sciatica; a few are primary, i.e. sciatic neuritis. Clinical manifestations 1. General symptoms ① Pain is mainly limited to the sciatic nerve distribution area, posterior thigh, posterior lateral calf and foot, and patients with severe pain may be in a unique posture; lumbar flexion, knee flexion, toe landing. If the lesion is located in the nerve root, the pain may increase when the pressure in the spinal canal increases (coughing, exertion); ② The degree of muscle weakness may vary greatly depending on the cause, location of the lesion, and the degree of damage, and there may be total or partial weakness or paralysis of the muscles innervated by the sciatic nerve; ③ There may or may not be pressure pain in the sciatic nerve trunk at the sciatic notch; ④ There is a positive sciatic nerve pull sign, Lasegue’s sign, and its isotonic sign. The presence of this sign often parallels the severity of the pain. The presence of this sign often parallels the severity of the pain. Local anesthesia of the sciatic nerve root or nerve trunk may disappear; ⑤ the Achilles tendon reflex is decreased or disappeared, and the knee reflex may be increased by stimulation; ⑥ there may be a decrease or disappearance of various sensations in the area of sciatic nerve innervation, including decreased vibration sensation in the outer ankle, and there may be very mild sensory disturbance; at least three of the above criteria are 1, 4, and 5. 2. Sciatica is often accompanied by various types of infections and systemic diseases, such as upper respiratory tract infections. Because the sciatic nerve is more superficial, it is susceptible to sciatic neuritis when exposed to moisture and cold, and systemic diseases should be noted when sciatic neuritis occurs with or without complications such as gliosis and diabetes. The clinical features are: sciatica is mostly unilateral, not accompanied by lumbar or back pain; the pain is usually persistent, but can also be episodic, and the symptoms increase when the pressure in the spinal canal increases, and can also radiate along the sciatic nerve pathway. Pain and muscle weakness are not parallel, generally pain is heavy, but muscle weakness is not obvious. In the acute stage, it is more difficult to judge motor function because of pain, foot drop, gastrocnemius and tibialis anterior muscle atrophy can be detected; Achilles reflex is reduced or disappeared, but Achilles reflex can also be normal, knee reflex is normal. Superficial sensory impairment is obvious. The pain can be relieved only after 2~3 weeks of treatment. 3. Secondary sciatica ①Lumbar disc prolapse: It is the most common cause of sciatica, mostly occurs in L4~5 and L5S1, about 1/3 of cases have a history of acute lumbar trauma, 80% of patients occur between 20~40 years old, but there are also 1/3 of cases without a history of trauma and physical labor, clinical characteristics are weeks or months of low back pain, followed by sciatica in one lower limb. In addition to the general symptoms of sciatica, physical examination also shows tension in the low back muscles, limitation of lumbar movement, scoliosis, and pressure pain in the spinous process of the lesion. In addition to sciatica, lumbar disc prolapse may also manifest as femoral neuropathy, amyotrophic lateral sclerosis syndrome, transverse myelopathy, conus caudalis syndrome or clinical manifestations similar to poliomyelitis. ② lumbar spine osteoarthropathy: mostly seen in people over 40 years old, subacute chronic onset, mostly with a history of long-term lumbar pain, difficulty in standing up after sitting for a long time, difficulty in sitting down after standing for a long time, clinically it can manifest as symptoms of sciatica and lumbar symptoms on one or both sides. (③) congenital malformation of lumbosacral spine: lumbosacralization, sacral lumbarization, L5 transverse process overgrowth, occult spina bifida, the latter may show sciatica in addition, often with a history of enuresis, physical examination often has foot deformity, lumbosacral skin abnormalities, such as a small concavity behind the anus, small angiomas on the sacral midline, this often objectively and accurately indicates the unhealed part of the vertebral plate. Sacroiliac arthritis: it is commonly rheumatoid and tuberculous lesions, which stimulate L4~5 nerve trunk when there is exudative destruction of joint capsule, 30%~40% of patients can have sciatica symptoms, and they are early symptoms, once the joint capsule is broken in late stage, sciatica is relieved, so patients with sciatica should check sacroiliac joint signs in detail when they visit the clinic.